We must know decimals to shelve books which have a classification by Dewey Decimals. In our school syllabus the strands are for decimals and operations are;

NS4.1 Recognises the properties of special groups of whole numbers and applies a range of strategies to aid computation

NS4.2 Compares, orders and calculates with integers
NS4.3 Operates with fractions, decimals, percentages, ratios and rates

And the link to the syllabus doc is
http://www.boardofstudies.nsw.edu.au/syllabus_sc/pdf_doc/03_maths_syl_number.doc